What actually triggers an IRS audit — and what doesn’t

There’s no single red flag

People talk about audit “triggers” as if one line on a return sets off an alarm. In practice, selection is quieter and more mechanical than that.

The IRS describes three main routes. Computer screening scores each return against statistical norms for similar returns, and the ones that look unusual get a closer look from a person, who decides whether an examination is worth the time. Related examinations pull in returns connected to a partner, business, or investor already under review. And a small number of returns are selected at random for research that helps the IRS refine its scoring.

Separately, the IRS matches what you report against the forms other people file about you: W-2s, 1099s, K-1s, brokerage statements. Strictly speaking, a mismatch letter isn’t an audit, but for most people it’s the most likely way the IRS will ever question their return.

Mismatches: the most common reason the IRS writes

When a payer reports income under your Social Security number or EIN and it doesn’t show up on your return, an automated system flags the gap. The result is usually a CP2000 notice proposing additional tax, interest, and sometimes an accuracy-related penalty.

A typical case: a consultant earns $140,000 from four clients, keeps good books, but pulls revenue from memory at filing time and misses an $18,000 engagement. The client’s 1099-NEC is already in the IRS system. Eighteen months later a CP2000 arrives proposing income tax and self-employment tax on the full $18,000, plus interest from the original due date.

Had the consultant reported it, the $18,000 would have been taxed the same way, but with no penalty exposure, no added interest, and no letter. Mismatch notices are among the most avoidable problems in tax, because the IRS already has the numbers — it’s simply checking whether yours agree.

Reporting thresholds changed recently, which is worth understanding. For payments made after December 31, 2025, businesses generally don’t have to issue a 1099-NEC or 1099-MISC unless payments to a recipient total $2,000 or more (up from $600). Payment apps and card processors issue a 1099-K only when payments exceed $20,000 and 200 transactions. Higher thresholds mean fewer forms, not less taxable income: every dollar is still reportable whether or not a form is issued.

The practical fix is to report income from your own records (bank deposits, invoices, merchant statements) and then reconcile to the forms you receive, rather than the other way around.

Patterns that tend to draw a closer look

None of these guarantees an audit. They’re the patterns that attract attention because they’re where errors and overstatements cluster.

• Business losses year after year, especially alongside high W-2 or investment income. The tax code presumes a profit motive if an activity shows a profit in at least three of five consecutive years; long losing streaks invite hobby-loss questions.
• Expenses that are large relative to revenue for your industry, such as travel or meals that look out of scale for a two-person firm
• Round numbers throughout, which suggest estimates instead of records
• A vehicle claimed as 100% business use, particularly when it’s the household’s only car
• Large noncash charitable gifts. Deductions over $500 require Form 8283, and items or groups of similar items over $5,000 generally need a qualified appraisal.
• Cash-heavy businesses, where income is harder to verify from third-party data
• Foreign accounts or assets that should have been disclosed but weren’t
• Big swings from year to year without an obvious explanation on the return

Issues specific to business owners

Owner-operated businesses have a few recurring exam issues that don’t come up for wage earners.

S corporation compensation is one. An owner who takes a small salary and large distributions reduces payroll tax, and the IRS knows it. A shareholder who pays himself $30,000 of wages out of $250,000 of profit is inviting a reasonable-compensation adjustment, which can reclassify distributions as wages subject to payroll tax plus penalties.

Worker classification is another. Treating people as contractors when they function like employees can lead to back payroll taxes. And commingled accounts — personal groceries paid from the business card, business income deposited to a personal account — make any exam longer and harder, because the examiner has to untangle everything before evaluating anything.

Finally, watch for personal costs running through the business: family phones, a spouse’s car, vacations with a single client lunch attached. Individually these look small, but an examiner who finds one tends to keep looking, and a pattern of them can turn a narrow exam into a broad one.

What mostly doesn’t matter

Filing an extension is not a known red flag. It’s a routine, legal tool, and a carefully prepared return filed in October is better than a rushed one filed in April. Just remember an extension gives you more time to file, not more time to pay.

Legitimate deductions you can support are not a problem. A home office you actually qualify for, business meals with a real business purpose, retirement contributions — claim what you’re entitled to. The risk isn’t the deduction; it’s the deduction you can’t document.

Getting a refund doesn’t make you a target, and neither does amending a return to fix a mistake. An amended return will be reviewed, but correcting an error on your own terms is almost always better than waiting for the IRS to find it.

Higher-income and more complex returns do receive more scrutiny on average. That’s not a reason to be anxious; it’s a reason to be organized.

How far back the IRS can look

The IRS generally has three years from the date you filed to assess additional tax. That stretches to six years if you left out more than 25% of the gross income you reported, and there’s no time limit for a fraudulent return or a return that was never filed.

In practice, the IRS says most audits cover returns filed within the last three years, and it usually doesn’t go back more than six. That’s why the IRS tells taxpayers to keep the records used to prepare a return for at least three years from filing. Records for property and investments should be kept longer — until the limitation period runs for the year you sell.

The real defense: a return that matches reality

You can’t control whether your return is selected. You can control how easy it is to defend. Before you file, run through a short checklist.

• Reconcile gross receipts to bank deposits and to every 1099 and 1099-K you received
• Report information returns even if you think they’re wrong, and get incorrect ones corrected or explain the difference
• Keep receipts, mileage logs, and contracts as you go, not reconstructed at filing time
• Keep business and personal spending in separate accounts
• Make sure large or unusual items have a paper trail you could hand to an examiner tomorrow
• For S corps, document how you arrived at the owner’s salary

When a second set of eyes helps

If your situation is complicated — multiple entities, big swings in income, foreign holdings, real estate, an S corp — a review by a CPA or enrolled agent is worth the time. At Tally Tax, a pre-filing review focuses on exactly what the IRS computers look for: income that doesn’t tie to third-party forms, expense ratios that stand out, and deductions without support behind them.

Frequently asked questions